A typical mammalian egg is surrounded by an outer layer of about 3,000 cumulus cells embedded in an extracellular matrix rich in the high molecular mass polysaccharide hyaluronic acid (HA). The sperm protein PH-20 has hyaluronidase activity and is present on the plasma membrane of mouse and human sperm (Lin Y et al (1994) J Cell Biol 125: 1157-63). PH-20 enables sperm to penetrate the egg's cumulus barrier, an essential step in the fertilization process. Biochemical characterization of PH-20 revealed the existence of both a soluble isoform and a glycosylphosphotidyl-inositol (GPI) linked isoform, in which PH-20 is bound to the membrane of the sperm acrosome (Thaler CD et al (1995) Biochemistry 34: 7788-7795). Sequence analysis indicates a GPI-anchor attachment site at amino acid position number 490 (Lin et al, supra).
HA acts in processes other than fertilization. It is found in the extracellular matrix of many cells, especially in soft connective tissues. HA has been assigned various physiological functions, such as in water and plasma protein homeostasis (Laurent TC et al (1992) FASEB J 6: 2397-2404). HA production increases in proliferating cells and may play a role in mitosis. It has also been implicated in locomotion and cell migration. HA seems to play important roles in cell regulation, development, and differentiation (Laurent et al, supra).
There is evidence for the expression of one or more non-testicular hyaluronidases. Evidence suggests that fibroblast HA degradation in the lung is mediated by a previously unrecognized lysosomal-type hyaluronidase whose activity is regulated by various cytokines (Sampson PM et al (1992) J Clin Invest 90: 1492-1503).
The venom of numerous animals including various snakes, bees, hornets, stone fish, platypus, scorpions, and lizards contain hyaluronidase. Hyaluronidase from the white face hornet is an allergen which induces an IgE response in susceptible people (Lu G et al (1995) J Biol Chem 270: 4457-4465). Venom hyaluronidase is thought to act as a "spreading factor", an aid in the diffusion of toxins. Researchers have found that lizard venom hyaluronidase promotes the spread of the hemorrhagic area in mice injected with hemorrhagic toxin (Tu AT et al (1983) Comp Biochem Physiol 76: 377-383).
Clinical Applications of Hyaluronidases
Effective contraception (100%) was obtained in male and female guinea pigs immunized with PH-20 (Primakoff P et al (1988) Nature 335: 543-546). 5 Based on these results researchers are continuing efforts to make an anti-sperm PH-20 contraceptive vaccine suitable for humans (Zhu X et al (1994) Arch Androl 33: 141-144).
HA has been chemically modified as a biomaterial for medical applications such as controlled drug release matrices, nerve guides, and wound dressings (Zhong SP et al (1994) Biomaterials 15: 359-365). These materials are being tested for their stability in cellular environments in which naturally occurring hyaluronidase is present.
HA has been used in clinical medicine. Its tissue protective and rheological properties have proved useful in ophthalmic surgery. Serum HA is diagnostic of liver disease and various inflammatory conditions, such as rheumatoid arthritis. Interstitial edema caused by accumulation of HA may cause disfunction in various organs (Laurent et al, supra).
HA is known to produce tumor cell adhesion and migration, and its small fragments are angiogenic. Lokeshwar VB et al (1996; Cancer Res 56: 651-657)reported a significant elevation of hyaluronidase activity in prostate tumor tissue compared to that in both normal prostate and benign prostate hyperplasia. Furthermore, hyaluronidase levels in tissues correlate well with tumor progression.
Clinical trials have shown that the combined therapy of vindesine, cisplatin, hyaluronidase, and radiation is well tolerated by most patients and highly effective against advanced squamous cell cancer of the head and neck (Klocker J et al (1995) Am J Clin Oncol 18: 425-428). In preclinical experiments the combination of hyaluronidase and the chemotherapeutic drug vinblastine had significant antitumor effects on SK-Mel-3 melanoma cells implanted in nude mice (Spruss T et al (1995) J Cancer Res Clin Oncol 121: 193-202). Furthermore, hyaluronidase was well tolerated in test animals and prevented the local inflammation reactions that are commonly seen after subcutaneous vinblastine injections.
As shown above, there are numerous clinical applications for known hyaluronidases and the existence of at least one additional human hyaluronidases has been inferred. The selective modulation of expression and activity of a novel hyaluronidase may allow successful management of diseases associated with HA, such as cancer and inflammatory conditions.